Apparatus and method for deposition for organic thin films

ABSTRACT

The invention provides apparatus and methods for organic continuum vapor deposition of organic materials on large area substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a division of U.S. patent application Ser.No. 13/864,527 filed on Apr. 17, 2013, which is a division of U.S.patent application Ser. No. 12/467,468 filed on May 18, 2009, now U.S.Pat. No. 8,440,021, which is a continuation-in-part of U.S. patentapplication Ser. No. 12/030,362 filed on Feb. 13, 2008, which claims thebenefit of U.S. Provisional Application No. 60/965,117 filed on Aug. 16,2007, the contents of which are incorporated herein by reference intheir entireties.

GOVERNMENT RIGHTS

This invention was made with Government support under contract No.FA9550-07-1-0364 awarded by the Air Force Office of Scientific Research.The government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for thedeposition of organic films. In particular, the invention relates toapparatus and methods for the deposition of substantially uniform thinfilms on large-area substrates, where the films may be neat or a mixtureof organic materials, such as a host/dopant mixture.

RESEARCH AGREEMENTS

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement:

-   Princeton University, The University of Southern California,-   The University of Michigan and Universal Display Corporation.-   The agreement was in effect on and before the date the claimed    invention was made, and the claimed invention was made as a result    of activities undertaken within the scope of the agreement.

BACKGROUND

Vacuum and low pressure thermal evaporation techniques have been used todeposit thin films of organic materials for a variety of organicelectronics, such as photovoltaics, organic light emitting devices(OLEDs), and thin film transistors, on research scales and, to a limitedextent, on industrial scales. Prior art techniques are prone to poormaterial usage, and cannot be scaled easily for large sized substrates.Substantially uniform deposition of organic thin films on large areasubstrates requires large, expensive deposition systems that requireincreased source material and cleaning.

SUMMARY

The present invention is directed to apparatus and methods for organiccontinuum vapor deposition (OCVD) and a source cell for vapordeposition. The organic continuum vapor deposition apparatus of theinvention includes a heated chamber, where all walls of the chamber areheated, a cooled substrate within the chamber, having a coating surface,at least one source cell, having an output opening directed into theheated chamber, at least one organic material source, at least oneheater, providing sufficient heat to convert the organic material intoan organic vapor, and at least one carrier gas source. The heatedchamber has a temperature sufficiently high to provide diffusive mixingof the gas and vapor from the source cell to provide a uniform organicflux of the organic vapor, above the cooled substrate, therebydepositing a substantially uniform film of the organic material oncoating surface of the cooled substrate. The diffusive mixing providesthe uniform flux in a relatively short distance from the outlet of thesource cell. Preferably, the source cell has an output directed at thesubstrate surface. Preferably, the source cell is positioned in a heatedback or end plate of the chamber. More preferably, the source cell ispositioned in a heated back or end plate of the chamber, and has anoutput directed at the substrate surface. Most preferably, the sourcecell is centered in a heated back or end plate of the chamber, and hasan output directed at the center of the substrate surface.

The method of the invention includes heating an organic material,forming an organic vapor, transporting the organic vapor in a carriergas from a source cell into a heated chamber, wherein all walls of thechamber are heated, heating the chamber sufficiently to form asubstantially uniform organic flux of the carrier gas and organic vaporby diffusive mixing of the gas and vapor within the heated chamber,directing the uniform organic flux to a cooled substrate, and depositingthe organic material onto a surface of the cooled substrate, therebyforming an organic film on the substrate. Preferably, the method mayfurther include directing a source cell output at the substrate surface.Preferably, the method may further include positioning the source cellin a heated back or end plate of the chamber. More preferably, themethod may further include positioning the source cell in a heated backor end plate of the chamber, and directing the at the substrate surface.Most preferably, the source cell is centered in a heated back or endplate of the chamber, and has an output directed at the center of thesubstrate surface

The source cell of the invention includes a hollow barrel, having a gasinput and a gas output, and a stopper at a first end of an actuator rod.The stopper and actuating rod have a first, closed position within thebarrel, thereby preventing gas flow through the gas output, and asecond, open position, allowing gas to flow from the gas output. Thestopper has a cross-sectional shape sufficiently similar to the gasoutlet shape to seal the gas outlet when the stopper is in the first,closed position.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an organic continuum vapor deposition (OVCD) chamberof the invention;

FIG. 2 is a plot of the uniformity of the flux against the length towidth ratio of the OCVD chamber;

FIGS. 3A and 3B illustrate the flux from two separate source cellshaving significantly different flow rates;

FIG. 3C is a plot of the deposition flux from each source cell againstthe distance from the source;

FIG. 4 illustrates an OCVD chamber, having a mixing chamber;

FIG. 5 illustrates an OCVD chamber, having stacked source cells;

FIG. 6 is a plot of the deposition flux against distance for centeredand off-center source cells;

FIG. 7 is a plot of the deposition flux against distance for OCVDchambers having heated and unheated source plates;

FIG. 8 is a plot of the deposition flux against distance for anoff-center directed source cell at three different flow rates;

FIG. 9 is a plot of the deposition flux against distance for twodifferent reactors having different source to substrate distances;

FIG. 10 is a plot of the deposition flux against distance for twodifferent reactors having heated and unheated source plates;

FIG. 11 illustrates a source cell, having a plug valve in the openposition;

FIG. 12 illustrates a source cell, having a plug valve in the closedposition;

FIG. 13 illustrates a source cell formed in a block; and

FIG. 14 illustrates an organic continuum vapor deposition (OVCD) chamberof the invention.

FIGS. 15A and 15B illustrate a source cell having a moveable holder forholding an organic material.

DETAILED DESCRIPTION

As used herein, the term “diffusive mixing” refers to mixing that is theresult of diffusion alone in contrast to, e.g., turbulent mixing.Diffusive mixing requires no artificial mixing, such as that providedby, e.g., a showerhead, propeller, or other turbulent mixing source.

As used herein, a “substantially uniform organic flux” refers to amixture of organic vapor and carrier gas in which the concentration ofthe organic vapor does not vary by more than about 20 mole percent.Preferably, the concentration of the organic vapor does not vary by morethan about 15 mole percent, more preferably, the concentration of theorganic vapor does not vary by more than about 10 mole percent, and,most preferably, the concentration of the organic vapor does not vary bymore than about 5 mole percent. Concentration gradients within the fluxare substantially absent. Also as used herein, a “substantially uniformorganic film” refers to a film of organic material, deposited on asubstrate, where the concentration and thickness of the depositedorganic material does not vary by more than about 20 mole percent.Preferably, the concentration and thickness of the deposited organicmaterial does not vary by more than about 15 mole percent, morepreferably, the concentration and thickness of the deposited organicmaterial does not vary by more than about 10 mole percent, and, mostpreferably, the concentration and thickness of the deposited organicmaterial does not vary by more than about 5 mole percent.

The terms “evaporation temperature” and “sublimation temperature” areused interchangeably herein, and refer to the temperature at or abovewhich an organic material produces a vapor of the organic material. Asused herein, the term “condensation temperature” refers to thetemperature at or below which an organic vapor will condense onto asurface to form a solid film. The condensation temperature is typicallyabout the same as the evaporation or sublimation temperature.

The invention provides apparatus and methods for organic continuum vapordeposition (OCVD) of organic materials on substrates. The inventionprovides diffusive mixing in a heated deposition chamber to create auniform organic flux that is directed to and deposited on a cooledsubstrate to form a substantially uniform film of organic material onthe substrate. The apparatus and methods of the invention may be scaledup to provide substantially uniform organic films on substratessignificantly larger than previously possible without the use of complexapparatus, such as shower heads. The apparatus and methods of theinvention may be used to provide substantially uniform organic films onsubstrates having a size on the order of substrates coated with priorart deposition apparatus and methods to substrates having at least onedimension greater than three meters. Substantially uniform organic filmsmay be deposited on substrates having at least one dimension of about0.25 m, 0.5 m, 0.75 m, 1 m, 1.25 m, 1.5 m, 1.75 m, 2 m, 2.25 m, 2.5 m,2.75 m, and larger with the apparatus and methods of the invention. Byheating the entire chamber, including the source or back plate, uniformorganic fluxes may be obtained with height or length to width ratios ofas low as about 0.75. As used herein, the source or back plate is thatwall of the chamber in which one or more source cells are positioned todirect carrier gas and organic vapor into the OCVD chamber and towardthe substrate. Heating the source or back plate sufficiently provides aheated source zone in the OCVD chamber where diffusive mixing occurs,establishing the desired uniform organic flux of the organic material tobe deposited. The method of the invention may be applied to a continuousprocess with a row of centrally located source cells or in a batchreactor with one or more source cells.

An OCVD chamber and substrate are illustrated in FIG. 1. The OCVDchamber 10 comprises a chamber 1, having a plurality of heated walls 2,at least one source cell 3, positioned through a heated source or backplate 4, such that the carrier gas and organic vapor are introduced intothe chamber 1. The source plate 4 may be, e.g., a ceramic block. Acooled substrate 5, having a surface to be coated 6, is placed withinthe chamber 1. The arrows in FIG. 1 generally illustrate the path ofgases and vapors within the OCVD chamber. The source cell 3 ispreferably positioned at approximately the center of the source or backplate, and has an axis that is normal to a point about at the center ofthe surface 6 of the substrate 5. Additional or alternative source cells7 and 8 may also be used to introduce organic vapor and carrier gas. Theadditional or alternative source cells may be placed in any convenientposition in the back plate 4, as illustrated by source cell 7, but arepreferably angled, such that the flow of gas and vapor are directed fromthe source cell toward the center of the surface 6, as illustrated bysource cell 8. Diffusive mixing of the gas and vapor from the sourcecells occurs in a source zone 9 in proximity to or adjacent to thesource or back plate 4. The simultaneous use of multiple source cellsallows for the deposition of doped materials in substantially uniformlayers. Preferably, each source cell has an axis through the outlet ofthe source cell that is directed to at least a portion of the substrate.

In the method of the invention, an organic material is heated in asource cell to a temperature higher than the sublimation temperature ofthe material to form a vapor. The organic material may be heated to formthe vapor by any means known in the art. Preferably, the organicmaterial is heated thermally. The organic vapor is transported from thesource cell into a heated OCVD chamber by a carrier gas, preferably, aninert carrier gas, such as nitrogen or helium, in the direction of thesurface of a cooled substrate, where the temperature of the surface ofthe cooled substrate is less than the condensation temperature of theorganic vapor. All of the walls, including the source or back plate, ofthe OCVD chamber are heated to a temperature higher than thecondensation temperature of the organic vapor, such that a substantiallyuniform organic flux of the organic vapor is formed within the chamberby diffusive mixing. The substantially uniform organic flux is directed,preferably, by a pressure differential within the deposition chamber, tothe cooled substrate. The organic vapor condenses of the surface of thecooled substrate, forming a substantially uniform organic film.

Preferably, every surface within the deposition chamber, except thecooled substrate, is heated to a temperature at least about 5° C. higherthan the condensation temperature of the organic vapor, more preferably,at least about 10° C. higher, and, most preferably, at least about 20°C. higher than the condensation temperature of the organic vapor.Organic materials that may be deposited with OCVD include, but are notlimited to, BCP (evaporation/sublimation temperature, T_(sub), of about160° to about 200° C.), pentacene (T_(sub) of about 260° to about 280°C.), NPD (T_(sub) of about 270° to about 300° C.), Alq₃ (T_(sub) ofabout 270° to about 300° C.), CuPc (T_(sub) of about 400° to about 460°C.), PTCBI (T_(sub) of about 420° to about 480° C.), and C60, (T_(sub)of about 420° to about 480° C.) A partial listing of these and othermaterials that may be deposited with OCVD is provided below. Adequatelyheating every surface within the OCVD chamber (other than the cooledsubstrate) sufficiently reduces or eliminates cold spots in the organicvapor and results in diffusive mixing of the organic vapor in thechamber, establishing the substantially uniform organic flux fordeposition on the substrate. It is noted that if, for example, only sidewalls of the chamber are heated, cold regions occur toward the endwalls. Moreover, by heating all of the walls of the chamber, as well asthe source cell, the vapor molecules remain continuously exposed to hightemperature until reaching the cooled substrate.

Preferably, the surface of the substrate is cooled to a temperature atleast about 50° C. lower than the condensation temperature of theorganic vapor, more preferably, at least about 100° C. lower, and, mostpreferably, at least about 150° C. lower than the condensationtemperature of the organic vapor. Even lower temperatures may be used,such as 200°, 250°, or 300° C. lower than the condensation temperature.The temperature of the substrate is preferably low enough that theconcentration of organic vapor molecules in a small volume directlyabove the cooled substrate may be approximated as zero for modelingpurposes.

The pressure within the source cell and in the chamber may be over anypractical range. As will be recognized by one of ordinary skill in theart, the pressure within the source cell will be greater than thatwithin the OCVD chamber. Useful pressures range from above oneatmosphere to less than 10 mtorr. Useful pressure ranges include 760 to100 torr, 100 to 10 torr, and 10 to 0.00001 torr.

The flow rate of the organic vapor in moles per second from a sourcecell may be expressed by Equation (1),

$\begin{matrix}{{r_{out} = \frac{P_{org}^{eq}\left( T_{cell} \right)}{\frac{\sqrt{2\pi \; M_{org}{RT}_{cell}}}{A_{source}} + \frac{{RT}_{cell}}{Q}}},} & (1)\end{matrix}$

where r_(out) is the evaporation rate in moles per second, P_(org) ^(eq)is the equilibrium vapor pressure of the organic material at temperatureT_(cell), the temperature of the source cell, Q is the flow rate of thecarrier gas in standard cubic centimeters per minute (sccm), A_(source)is the surface area of the source of organic material, M_(org) is themolar molecular weight of the organic material, and R is the molar gasconstant

To obtain a similar deposition rate with a larger substrate, theevaporated flux of organic vapor must be increased by a factorproportional to the change in substrate area, which is given by equation(2),

$\begin{matrix}{{r_{2}^{out} = {\frac{A_{2}^{sub}}{A_{1}^{sub}}r_{1}^{out}}},} & (2)\end{matrix}$

where r₁ ^(out) is the evaporation rate required for the firstsubstrate, r₂ ^(out) is the evaporation rate for the second substrate,A₁ ^(sub) is the surface area of the first substrate, A₂ ^(sub) is thearea of the second substrate. Equations (1) and (2) were solvednumerically to determine the flow rate and/or the growth temperaturerequired for a given substrate size.

For example, coating a substrate having an area of 25 cm² requires a Qof about 25 sccm, a T_(cell) of about 650 K (377° C.), and a sourcearea, A_(source), of about 0.1 cm². To scale up the apparatus for a 1.5m square substrate requires a Q of about 2,000 sccm, a T_(cell) of about660 K (387° C.), and a source area, A_(source), of about 100 cm².

Modeling shows that the uniformity of the flux, and, thus, the depositedfilm, varies with the materials deposited, the flow rate, Q, and thelength to width ratio, L/W, of the deposition chamber, where the length,L, is the source to the substrate distance, and the width, W, is thewidth the deposition chamber. Modeling of the apparatus and methods ofthe invention are described below. Results for the variation in theuniformity of the flux produced as a function of Q and L/W isillustrated in FIG. 2. FIG. 2 provides a plot of the relative deviationof the organic flux against L/W for a fixed W. The modeling parametersused in preparing the graph of FIG. 2 were as follows:

Carrier gas: Nitrogen;

Pressure: 1.33 Pa (1×10⁻² torr);

Heat capacity: 1000 J/kg-K;

Substrate temperature: 300K (27° C.);

Wall temperature: 650K (377° C.);

Viscosity (300K): 1.73×10⁻⁵ kg/m-s;

Density: P/(RT) kg/m²;

Thermal conductivity (300K): 0.25 W/m-K; and

Deposited material molecular weight: 200 g/mole.

The y-axis of the plot of FIG. 2 is the relative deviation, i.e., thestandard deviation of the flux divided by the mean flux of thedeposition profile. For a given Q, the uniformity of the depositionimproves initially with increasing values of L/W, and asymptoticallyapproaches a constant value. Thus, increasing L eventually provides noadvantage, as there is no significant additional improvement in theuniformity of the organic flux or the deposition.

The uniformity of the deposition may also deteriorate with increasingsource flow rate, requiring a higher L/W for a given uniformity. Asillustrated in FIG. 2, the uniformity is significantly better for a Q of100 sccm than for a Q of 1,000 or 4,000. As will be recognized by thoseskilled in the art, the uniformity required will depend on theparticular application. For the model deposition illustrated in FIG. 2,uniformities preferably have a STD/mean value of less than about 11.5percent, as illustrated by the upper dashed line in the plot of FIG. 2,and, more preferably, of less than about 8.5 percent, as illustrated inthe lower dashed line in the plot of FIG. 2. Therefore, increasing theflow rate, Q, provides a faster deposition rate, but also requires alarger L/W value, and, thus, a larger deposition apparatus. Thus, theL/W of a particular OCVD chamber and the desired uniformity of the fluxand resulting film will determine the flow rate, Q, for a given set ofdeposition conditions. Similarly, for the design of an OCVD chamber, thedesired deposition rate, will determine the required Q, and, thus, theL/W of the chamber.

Where a doped material from two separate source cells is deposited on asubstrate, uniformity is diminished when the Q of the two sources issignificantly different. As will be recognized by those skilled in theart, this arises when a host and at least one dopant are depositedsimultaneously. FIG. 3 illustrates the results of a simulation of anOCVD chamber 30 in which a host material and dopant are introducedsimultaneously, and the Q of the host material from a first source 31 is10 times larger than the Q of dopant from a second source 32. Asillustrated in FIGS. 3A and 3B, host and dopant materials are introducedinto an OCVD chamber 30 from the first source 31 and the second source32, respectively. FIG. 3A shows the concentration of the host material33 within the chamber 30, and FIG. 3B shows the concentration of thedopant material 34, where the flow rate, Q, of the host from the firstsource is 100 sccm, and the Q of the dopant is 10 sccm. Plots of thedeposition flux of the host 33, lower plot, and the dopant 34, upperplot, at a given distance from the source are provided in FIG. 3C. Asclearly illustrated in FIG. 3, the uniformity of the dopant issignificantly worse that that of the host, as the dopant flux 34 isdisplaced by the host flux 33 within the OCVD chamber 30, as the hostflux 33 has a significantly higher flow rate, Q. Thus, to obtain asubstantially uniform coating of host and dopant materials, the carriergases for the host and dopant materials are preferably not introducedfrom separate sources at significantly different flow ratessimultaneously.

Substantially uniform fluxes and coatings of doped host materials may beobtained by premixing the host and dopant materials before the organicvapors and carrier gases are introduced into the OCVD chamber, or by“stacking” the host and dopant sources. An OCVD apparatus in which hostand dopant are premixed with carrier gas is illustrated in FIG. 4. Asillustrated, in FIG. 4, the host and dopant are introduced with acarrier gas from source cells 41 and 42, respectively, into a mixingchamber 43. The walls 44, including source plate 44 a, of the mixingchamber are preferably heated to prevent condensation of the organichost and dopant materials on the walls 44. The temperature of the walls44 should be at a temperature higher than the lower of the condensationtemperatures of the host and dopant. The mixture of carrier gas, dopant,and host materials is then introduced into the deposition chamber 45,having heated walls 46, such that a substantially uniform organic fluxis formed for deposition of a substantially doped film on the cooledsubstrate 47.

FIG. 5 illustrates a “stacked” apparatus 50 in which the source cells 51and 52 are placed in series. Carrier gas is introduced first into thesource cell 51, which contains the organic material, either host ordopant, having the lower sublimation temperature. The resulting mixtureof carrier gas and organic vapor is then introduced into source cell 52,which contains the organic material, either host or dopant, having thehigher sublimation temperature. The mixture of carrier gas, host vapor,and dopant vapor is then introduced into the heated deposition chamber53, forming a substantially uniform organic flux that is deposited onthe cooled substrate 54.

The conditions within an OCVD chamber have been modeled for differentapparatus configurations, source flow rates, Q, and pressures. Modeledconfigurations include centered source cells, having an axis normal tothe surface of the cooled substrate, off-center source cells, having anaxis normal to the surface of the cooled substrate, angled, off-centersource cells, and OCVD chambers, having heated and unheated sourceplates. The modeled system was highly coupled and highly non-linear.Model simulations were obtained by solving the two-dimensional continuumequations for energy (temperature), mass (concentration and surfaceflux), and Navier-Stokes momentum (velocity). Dependent variables of theequations were the velocity field, U, the pressure, P, the temperature,T, and the concentration or flux, C. The modeled systems followedpseudo-compressible dynamics in which the variable dependencies were asfollows:

μ(viscosity)=f(T);

k(thermal conductivity)=f(T);

ρ(density)=f(T,P);

D(diffusivity)=f(T,P); and

U(vector velocity)=f(μ,ρ,T,P).

The governing equations for the modeling were as follows:

The equation for the mass balance of the organic material is

∇·(−D _(i) ∇C _(i) +C _(i) U)=0;

The equation for the energy balance of the nitrogen carrier gas is

∇·(−k∇T+ρCpTU)=Q;

The equation for the momentum balance, i.e., Navier-Stokes, is

−∇·μ(∇U+(∇U)^(T))+ρ(U·∇)U+∇P=F; and

The continuity equation is

∇·U=0.

The model was constructed and solved numerically using Femlab®,available from COMSOL of Burlington, Mass. Femlab® is a multiphysicsmodeling and analysis software package that automates methods ofparametric analysis and design optimization. Femlab® was used to model a2 meter wide by 1.8 meter chamber with a 1.6 meter wide substrate. Theboundary conditions for the model, i.e., the conditions at each surfacewithin the OCVD chamber, were based on the assumptions that thetemperature of the substrate sufficiently low for the concentration oforganic molecules directly above the substrate to be approximated aszero, and that there is no slip at the boundaries, i.e., U_(x,y)=0. Thatis, there was no net velocity at the boundary, such that the materialdoes not penetrate the surface or move along the surface. The boundaryconditions for the simulation were as follows: For the surface of thecooled substrate, U_(x,y)=0 (no slip), T=T₀₀, and C=0; for the sidewalls, U_(x,y)=0, T=T₀, and the wall was totally insulating; for thesource plate, U_(x,y)=0, T=T₀ or T₀₀, depending on the modeledconfiguration, and the source plate was totally insulating; and, for theoutput of the source cells, U=U₀→Q, T=T₀, and the flux=U₀*C₀. Themodeling parameters used were as follows:

Flow rate: 25, 100, 2000, 4000, and 10,000 sccm;

Carrier gas: Nitrogen;

Pressure: 1.33 Pa (1×10⁻² torr) and 133 Pa (1 torr);

Heat capacity: 1000 J/kg-K;

Substrate temperature: 300K (27° C.);

Wall temperature: 650K (377° C.);

Viscosity (300K): 1.73×10⁻⁵ kg/m-s;

Density: P/(RT) kg/m³;

Thermal conductivity (300K): 0.25 W/m-K; and Deposited materialmolecular weight: 200 g/mole.

The simulations indicate that a centered source cell provides asubstantially uniform flux within the OCVD chamber and a symmetric,undistorted boundary layer near the cooled substrate. In contrast, anoff-center source cell results in a distorted boundary layer thatprovides a non-uniform deposition. As illustrated in FIG. 6, at lowsource flow rates, the deposition profile is substantially independentof source cell location. However, at higher flow rates, film uniformityis significantly worse for an off-center source. This effect isintensified where the source plate is not heated (lower plot), asillustrated in FIG. 7, but may be minimized by pointing source towardssubstrate center, as illustrated in FIG. 8 for three different Q values.The top plot of FIG. 8 corresponds to a Q of 100 sccm, the middle plotcorresponds to a Q of 4,000 sccm, and the lowest plot corresponds to a Qof 10,000 sccm. As illustrated in FIG. 9, increasing the source tosubstrate distance does not completely correct for the distortedboundary layer that results form an off-center source cell that is notdirect at the center of the substrate. The boundary layer near thesurface of the cooled substrate remains distorted, resulting in a lossof uniformity. The deposition flux for the longer reactor is the lowerplot in FIG. 9. As seen in FIG. 9, the gains obtained by increasing L/Wdiminish after a point. The higher noise for the longer reactor in FIG.9 is the result of the simulation mesh, which spreads out due to thelarger simulation area.

FIG. 10 illustrates the results for the simulated scaling of OCVDchambers, having heated (upper curve) and unheated (lower curve) sourceplates and a centered source cell. The modeled OCVD chamber had a widthof 3 meters and a source to substrate distance of 2.5 meters for asubstrate having a width of about 2.5 meters. The source flow rate, Q,was 4,000 sccm, and the chamber pressure was 1.33 Pa. The simulatedchamber, having the heated source plate provided a substantially uniformdeposition profile, substantially the same as the smaller chamber.Again, the heated the source plate provided a significantly betteruniformity than the unheated plate. The variation in the uniformity ofthe deposition with the heated back plate was 3 percent, compared with 7percent for deposition with the unheated back plate.

The simulations indicate that a chamber L/W of 0.75 provides excellentdeposition uniformity, particularly for substrates having a size about0.6 that of the chamber width. Directed off-centered sources can be usedwhere multiple sources are required. The best uniformity and materialusage is obtained using a heated source plate.

The present invention also provides a source cell of an OCVD system,having a plug valve for the control of the flow of vapor and/or gasthrough the barrel of the source cell into the deposition chamber.Typically, the source cell is heated to a temperature greater than thesublimation temperature of a source of organic material placed in thesource cell to provide an organic vapor. Preferably, the flow iscontrolled with a stopper positioned within the barrel.

Source cells comprising the stopper of the invention in the open andclosed positions are illustrated in FIGS. 11 and 12, respectively. Asillustrated in FIGS. 11 and 12, a preferred source cell 110 comprises abarrel body or shell 111, a stopper head 112, an actuator rod 113, a gasinlet 115, and a gas outlet 116. Preferably, the source cell furthercomprises a bypass line 114 that is open when the stopper head is in theclosed position, and closed when the stopper head 112 is in the openposition. This prevents a pressure build-up or back flow within thesource cell 110 when the stopper 112 is in the closed position. When thestopper head 112 is in an intermediate position, such that the gas flowis not cut off completely, but is restricted, the bypass line 114 isalso preferably partially closed to maintain the pressure with in thesource cell 110. Preferably, the temperature of the source cell 110 ator near the gas outlet 116 is substantially the same as the temperaturewithin the source zone of the OCVD chamber, and the temperature of thesource cell 110 at or near the gas inlet 115 is substantially roomtemperature. The temperature of the source cell 110 is thus hot at thelocation of the valve, where such elevated temperature may be required.In this manner, a hot valve is provided at the point of use, i.e., atthe gas entrance to the chamber.

Although the inlet to the barrel body 111 of FIGS. 11 and 12 is offset,it should be appreciated that, according to other examples, the inlet isnot offset. For example, the inlet may be concentric with thelongitudinal axis of the barrel body 111. Moreover, it should beappreciated that while the barrel body 111 of FIGS. 11 and 12 has asingle gas inlet, the barrel body of other examples may have multipleinlets.

Movement of the stopper head 112 may be manual or automated, and may beachieved by any means known in the art. Preferably, an actuatormechanism (not shown) is attached to the actuator rod 113, and isconfigured to move the actuator rod 113 and head 112. The actuatormechanism may be of any useful type known in the art. Examples ofautomated actuator mechanisms include, but are not limited to,pneumatic, hydraulic, and electronic. Electronic mechanisms includestepper motors that can be digitally controlled, allowing precisecontrol of the stopper head 112 position.

Preferably, the stopper head 112 and the gas outlet 116 havecorresponding or compatible shapes. Thus, when the stopper is positionedin the closed position, the stopper head 112 seals the gas outlet 116.The contact seal between the stopper head 112 and the barrel body 111 issufficient to cut off the flow of gas through the outlet 116.

The shape of the stopper head may be, but need not be, the same as thegas outlet 116. The stopper head may be, e.g., conical, frustoconical,or spherical. All that is required is that that portion of the stopperhead 112 that contacts the barrel 111 has a shape that will seal theoutlet along a continuous line of contact, and prevent any gas flowthrough the gas outlet 116.

Preferably, the shape of the stopper head 112 and the outlet 116 providefor the self-centering of the stopper head 112 within outlet 116. Thus,the interior wall 117 of the body need not be conical, as illustrated inFIGS. 11 and 12. Any shape that will allow at least a portion of thestopper head 112 to enter and form an intimate seal with the edge of theoutlet 116, cutting off the gas flow, is useful in the invention. Forexample, as illustrated in FIGS. 11 and 12, a portion of the stopperhead 112 is conical and the outlet 116 is circular in shape. As thestopper head 112 is directed into the outlet 116, the cone shape of thestopper will guide the stopper into the outlet, naturally resulting in aself-centered alignment. Stopper 112 shapes include, but are not limitedto, generally spherical, hemispherical, and conical shapes. The edge ofthe gas outlet 116 may beveled to match the shape of the stopper head112. In contrast to typical needle-type valves, e.g., multiple-turnneedle valves, that have large contact areas at the sealing seat, thecontact area between the stopper head 112 and the outlet 116 isrelatively small. This may be advantageous, as temperature changes andassociated thermal expansion of the materials may be less likely tocause the stopper head to jam within the outlet 116, thus resulting in amore reliable valve. Moreover, it may be advantageous to position thestopper head 112 in an open position, as shown, e.g., in FIG. 11, whenthe temperature of the source cell 110 is adjusted, as this may furtherlimit the possibility of jamming due to thermal expansion. In thisregard, the materials may have different coefficients of thermalexpansion.

The stopper head 112, actuator rod 113, and source cell 111 can be madefrom any useful material known in the art that can withstand thetemperature and pressure conditions to which the barrel 110 issubjected, and can provide a seal between the head 112 and outlet 116.Useful materials include, but are not limited to, metal, such asaluminum, titanium, and stainless steel, glass, quartz, ceramics andcomposites. Forming the stopper head 112 and the sealing surface of theoutlet 116 of the source cell 111 from different materials may bedesirable, as this may reduce galling and/or binding at the sealingseat. As a particularly advantageous arrangement, a quartz stopper mayform a sealing seat with a stainless steel portion of the source cell.

Source cells in accordance with the invention may be subjected totemperatures of from about 0° to about 500° C.

Barrels in accordance with the invention will often be exposed to atemperature gradient from the inlet end of the barrel to the outlet end.This allows the end of the actuator rod 113 attached to the actuatormechanism to be at room temperature, while the output end is at theoperating temperature of the deposition chamber.

This type of valve is highly suitable for high temperature chambers witha temperature gradient along the flow direction. The stopper head of thevalve can withstand a high temperature environment while the other endof the actuator rod is kept cool. Sealing of the chamber relies on theseal between the actuator rod and the chamber, shown at the inlet end ofthe source cell as illustrated in FIGS. 11 and 12, which can be at roomtemperature to reduce chance of failure. The motion of the push-rodtogether with the head may be easily controlled by a mechanism outsidethe chamber at room temperature. By disposing the high-temperaturestopper away from the actuators, the reliability of the valve may belargely improved when working in high temperature applications. Becausethe temperature of the stopper head and the wall opening are at aboutthe same temperature, this valve design may also minimizes the chance ofthe stopper becoming stuck during motion caused by different thermalexpansions between the moving and static parts.

The flow rate of gas through the barrel is a function of the pressureoutside the inlet 115 and the outlet 116, the size of the inlet andoutlet, and the position of the stopper head 112 relative to the outlet116. When the stopper head 112 is positioned near or partially withinthe outlet 116, gas flow through the source cell 110 and outlet 116 willbe restricted. Positioning the stopper head 112 away from the outlet 116a sufficient distance will allow the maximum flow possible for thebarrel 110 for the gas pressures at the inlet 115 and outlet 116.

Preferably, organic materials for deposition within the depositionchamber are placed in the heated end of the barrel. Carrier gas can thenbe introduced through the inlet 115, mixed with organic vapor from theheated organic material, and introduced into the deposition chamberthrough the outlet 116. Sealing the outlet 116 of the barrel 110 withthe stopper head 112 provides for the rapid switching of organicmaterials within a barrel.

The valve region of the source cell 110 may be heated by the back plateof an OCVD chamber or a separate heating element.

The source cell 110 may also be used to introduce a non-processing gasfor balancing pressure or for dilution at a controlled rate. With thesource cell of the invention, the flow rate need not be controlled byvarying the source pressure of the gas. Instead, the flow rate can becontrolled by precise positioning of the stopper head.

Referring to FIG. 13, a source cell 210 is positioned in a heated block250. The block 250 may be, e.g., a ceramic block. The heated block 250acts as a heat source for the source cell 210 at the outlet, or valveregion, thereof. The heated block 250 may be, e.g., a back plate of anOCVD chamber. In this example, the source cell is formed directly intothe source block. Because the heat source is located adjacent the valveregion of the source cell, the opposite, or inlet region may bemaintained at a substantially lower temperature, e.g., at or close toroom temperature.

An OCVD chamber and substrate are illustrated in FIG. 14. The OCVDchamber 310 comprises a chamber 301, having heated side walls orsurfaces 302, a source cell 303, positioned through a heated back plate304, such that the carrier gas and organic vapor are introduced into thechamber 301. A cooled substrate 305, having a surface to be coated, isplaced within the chamber 301. The side walls 302 and the back plate 304are heated by a heater 340. In this example, the back plate or wall 304,the side walls 302, and the front wall are all heated by the heater 340,which supplies heat through all of the walls. It should be appreciatedthat the heater may contain multiple and/or separate heating elements.The heating elements may be of any appropriate type, e.g., electricheating elements. The heating element may be, e.g., located within eachwall or be located at an outer surface of each wall.

FIGS. 15A and 15B show cross-section side views of an example embodimentof a source cell. Source cell 120 includes a barrel body 122 having atits proximal end, a gas inlet 140, and at its distal end, a gas outlet128. A carrier gas flows into source cell 120 from gas inlet 140 andflows out through gas outlet 128. Gas inlet 140 also has a bypass line142 to prevent pressure build-up or back flow within source cell 120. Astopper head 126 is shaped to fit into and seal gas outlet 128. Stopperhead 126 is moved back and forth by actuator rod 127 to open and closegas outlet 128. Movement of stopper head 126 may be manual or automated(e.g., by a motorized actuator mechanism).

Source cell 120 is configured to provide a temperature gradient 144within the chamber 132 of barrel body 122. Temperature gradient 144rises from a proximal location within chamber 132 to a distal locationwithin chamber 132. Temperature gradient 144 can begin and end anywherealong the length of barrel body 122 and can be established using anysuitable heating source, including those described above. For example,temperature gradient 144 is provided by a heating coil 124 within thewall of barrel body 122, with the coils increasing in density as itapproaches gas outlet 128.

Source cell 120 also has a holder 130 located within chamber 132 ofbarrel body 122 for holding the organic source material. Holder 130moves back and forth along a path from a proximal location to a distallocation in chamber 132. Holder 130 is connected to an actuator rod 136that moves holder 130 back and forth along the central longitudinal axisof barrel body 122. Holder 130 also has a temperature sensor 134, e.g.,a thermocouple, for sensing the temperature inside barrel body 122 inthe vicinity of holder 130.

In operation, with a rising temperature gradient 144 established withinchamber 132, holder 130 containing the organic source material is movedback and forth within chamber 132 to expose the organic source materialto the desired temperature. The position of holder 130 can be adjustedaccording to the temperature sensed by temperature sensor 134. Thus, theevaporation rate of the organic source material can be rapidlycontrolled by adjusting the position of holder 130 within temperaturegradient 144. By controlling its evaporation rate, the deposition rateof the organic source material can be controlled to allow for improvedfilm morphology.

Also, this configuration allows for the organic source material to bequickly cooled after deposition is complete by withdrawing holder 130 toa cooler temperature. For example, referring to FIG. 15A, during filmdeposition, stopper head 126 is in an open position and holder 130 isheld within temperature gradient 144 to vaporize the organic sourcematerial. Referring to FIG. 15B, after film deposition is complete,stopper head 126 is moved to a closed position and holder 130 isretracted to the cooler proximal end of barrel body 122 to preventthermal degradation of the organic source material.

Materials that can be deposited with the apparatus and methods of theinvention include, but are not limited to,

-   CBP: 4,4′-N,N-dicarbazole-biphenyl-   m-MTDATA

4,4′,4″-tris(3-methylphenylphenlyamino)triphenylamine

-   Alq₃: 8-tris-hydroxyquinoline aluminum-   Bphen: 4,7-diphenyl-1,10-phenanthroline-   n-BPhen: n-doped BPhen (doped with lithium)-   C60-   F₄-TCNQ: tetrafluoro-tetracyano-quinodimethane-   p-MTDATA: p-doped m-MTDATA (doped with F₄-TCNQ)-   Ir(ppy)₃: tris(2-phenylpyridine)-iridium-   Ir(ppz)₃: tris(1-phenylpyrazoloto,N,C(2′)iridium(III)-   BCP: 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline-   TAZ: 3-phenyl-4-(1′-naphthyl)-5-phenyl-1,2,4-triazole-   CuPc: copper phthalocyanine.-   ITO: indium tin oxide-   NPD: N,N′-diphenyl-N—N′-di(1-naphthyl)-benzidine-   TPD: N,N′-diphenyl-N-N′-di(3-toly)-benzidine-   BAlq: aluminum(III)bis(2-methyl-8-quinolinato)4-phenylphenolate-   mCP: 1,3-N,N-dicarbazole-benzene-   DCM: 4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2-methyl)-4H-pyran-   DMQA: N,N′-dimethylquinacridone-   PEDOT:PSS: an aqueous dispersion of poly(3,4-ethylenedioxythiophene)    with

polystyrenesulfonate (PSS)

-   Pentacene-   PTCBI: 3,4,9,10-perylenetetracarboxylic bisbenzimidazole-   Ir(4,6-F₂ppy)₂(BPz₄) iridium(III)    bis(2-(4,6-difluorphenyl)pyridinato-N,C²)η²-N,N′-(tetrakis(1-pyrazolyl)borate)-   p-(SiPh₃)₂Ph p-bis (triphenylsilyl)benzene-   DEC dibenzo-18-crown-6-   F₃ 2,2′:7′,2″-Ter-9dimethyl-fluorene-   SC5 2,4,6-triphenyl-1-biphenyl-benzene-   P4N 1,2,3,4-tetraphenylnapthalene

It should be appreciated that the apparatus and methods described hereinmay be applied in the deposition of non-organic materials.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art. Therefore, it is intended that the appended claimscover all such modifications and embodiments as falling within the truespirit and scope of the present invention.

What is claimed is:
 1. A method of depositing an organic thin film ontoa substrate, comprising: heating an organic material, forming an organicvapor; transporting the organic vapor in a carrier gas from a heatedsource cell into a chamber, wherein a back plate of the chamber isheated, the source cell being positioned at the back plate; heating thechamber sufficiently to form a substantially uniform organic flux of thecarrier gas and organic vapor by diffusive mixing of the gas and vaporwithin the heated chamber; directing the uniform organic flux to acooled substrate; and depositing the organic material onto a surface ofthe cooled substrate, thereby forming an organic film on the substrate.2. The method of claim 1, wherein the chamber is heated by supplyingheat from all walls of the chamber.
 3. The method according to claim 1,wherein the chamber has a length to width ratio of at least about 0.75.4. The method according to claim 1, wherein the uniform organic flux isa steady state flux.
 5. The method according to claim 1, wherein theuniform organic flux is directed to the cooled substrate by a pressuredifferential.
 6. The method according to claim 1, further comprisingpositioning the source cell, so that the output is aligned with thecenter of the cooled substrate.
 7. The method according to claim 1,further comprising depositing a plurality of organic materials from aplurality of source cells.
 8. The method according to claim 7, furthercomprising depositing the plurality of organic materials successively.9. The method according to claim 7, further comprising depositing theplurality of organic materials simultaneously.
 10. The method accordingto claim 9, further comprising forming the organic vapors of the organicmaterials in a series of successive source cells, wherein organic vaporproduced in one cell passes through at least one additional source cell.11. The method according to claim 1, further comprising controllingvapor flow from the source cell with a valve within a source cell. 12.The method according to claim 1, further comprising controlling vaporflow from a source cell by moving a stopper relative to an opening inthe source cell, wherein the stopper has a shape that corresponds tothat of the opening, and stops the vapor flow when the stopper is movedfully into the opening.
 13. The method according to claim 12, furthercomprising opening a bypass line when the opening of the source cell isclosed by the stopper.
 14. The method according to claim 1, furthercomprising maintaining the cooled substrate at a temperaturesufficiently low to reduce the organic material concentration in aregion directly above the surface of the cooled substrate to aconcentration substantially less than the organic material concentrationin the rest of the heated chamber.
 15. The method according to claim 1,further comprising maintaining a flow rate of the organic vapor andcarrier gas sufficient to maintain the organic vapor in the heatedchamber at a substantially uniform concentration other than in theregion directly above the surface of the cooled substrate.